This study explores the effect of southward expansion of Northern Hemisphere (American) mid-glacial ice sheets on the global climate and the Atlantic Meridional Overturning Circulation (AMOC) as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 (36 ka) and 5a (80 ka) are performed with an atmosphere–ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 and 2.2 ^∘C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3 % in MIS3, whereas it strengthens by 16 % in MIS5a, both of which are consistent with an estimate based on ²³¹Pa ∕ ²³⁰Th. Sensitivity experiments extracting the effect of the southward expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 ^∘C, contributing to about 40 % of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 ^∘C over the Southern Ocean as a result of colder North Atlantic Deep Water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles and, hence, compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by two competing effects: surface wind and surface cooling. The relative strength of surface wind and surface cooling effects depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.

中文翻译：

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中冰期冰盖对深海环流和全球气候的影响

这项研究探讨了北半球（美国）中部冰盖向南扩张对全球气候和大西洋子午翻转循环（AMOC）的影响，以及冰盖改变AMOC的过程。为此，使用大气-海洋总循环模型对海洋同位素阶段（MIS）3（36 ka）和5a（80 ka）进行了模拟。在MIS3和MIS5a模拟中，全球平均温度由5.0和2.2降低 ^∘分别C，与前工业气候模拟比较。MIS3中的AMOC降低了3％，而MIS5a中的AMOC则提高了16％，这两者均与基于²³¹ Pa  ∕  ²³⁰的估计一致 。灵敏度实验提取MIS5a冰川片材MIS3的向南膨胀效应示出了全球冷却的1.1  ^∘ C，贡献于总表面冷却从MIS5a到MIS3的约40％。这些实验还表明，冰盖膨胀导致表面冷却 ^2∘。由于北大西洋深水较冷，南海上空出现C。我们发现，中冰期冰盖的向南扩张对AMOC的影响很小。部分耦合的实验表明，冰川冰盖对全球表面的冷却趋向于通过增加两极的海冰来降低AMOC，从而补偿了北大西洋上空增强的表面风的强化作用。我们的结果表明，冰川冰盖对AMOC的总影响取决于两个相互竞争的影响：地表风和地表冷却。地表风和地表冷却效应的相对强度取决于冰盖的构造，当冰面范围的变化明显时，地表冷却的强度可以与地表风的强度相当。